The present invention relates to a method and apparatus for producing a dry formed web from fibrous material. Both paper and nonwoven webs may be produced by this dry forming process. Dry forming can result in significant energy savings when compared with conventional wet forming systems. Wet formed webs are produced by mixing fibers with water to form a slurry and laying this slurry on a forming wire. The water is then removed from the newly formed web by mechanical and thermal means. Typically, it will take 100 tons of water to make one ton of paper. A great amount of energy is required both, to pump this water, and to heat dryers to remove residual water. Further energy is required to treat waste water before it is discharged. Present concern over energy conservation and water pollution has caused attention to be focused on energy efficient, "dry" paper formation processes.
In typical prior art dry forming processes, air is substituted for water as the carrying fluid. Many formers have been built in which fibers are carried by a turbulent air flow to a forming wire, where they are disposited. Usually a vacuum box is placed below the forming wire to suck air through the wire. The vacuum assists in the formation of the web and also collects the fines and fibers which pass through the forming wire. The air, fibers and fines collected by the vacuum means are then usually recirculated to an entrainment zone where "white air" from the forming process is mixed or blended with fibers from a classifier or defiberizer.
The newly formed web is then processed further. Further treatment is quite arbitrary and depends on desired sheet characteristics as well as the properties of the starting material. Typical treatment to consolidate the web includes embossing, pressing, and binding. After these processing steps, the web is a coherent and mechanically stable product.
Another prior art forming arrangement is taught by Kroyer U.S. Pat. No. 3,575,749. It is known, for example, that an electrostatic potential can be used to deposit fiber or binder on a moving band. The fiber or binder receives a charge of one polarity and the band receives a charge of the opposite polarity. In this prior art arrangement, there exists an attraction between the fibers or binder and the surface upon which it is to be deposited. The drawback of such an arrangement it that the web formed is not uniform.